HAT-P-39 b

Astrophysical Synthesis & Habitability Characterization

HAT-P-39 b is a confirmed gas giant exoplanet orbiting the star HAT-P-39, located approximately 2273.3 light-years (697 parsecs) from the Solar System. First announced in 2012 by HATNet using the Transit detection technique (producing an estimated primary transit depth of 0.987% across the stellar disk), this world measures 17.609 Earth radii (1.57 Jupiter radii) and has a measured mass of 190.372 Earth masses (0.6 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.19 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.61 g⊕ (5.98 m/s²), and an escape velocity of 36.8 km/s.

In its orbital architecture around HAT-P-39, HAT-P-39 b completes one full revolution every 3.544 Earth days at a semi-major axis of 0.0509 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 156.3 km/s (compared to Earth's 29.8 km/s). The orbit is modeled as circular (e = 0.00), maintaining a constant stellar distance throughout its year.

⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1752 K (+1479°C / +2694°F) and receiving 1,915.69 S⊕ (~2,607,259 W/m²), HAT-P-39 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.

The host star HAT-P-39 is classified as a stellar host with an effective photospheric temperature of 6,430 K, a radius of 1.625 R☉, a mass of 1.404 M☉, an estimated bolometric luminosity of 4.05 L☉. Stellar evolution modeling indicates an estimated stellar age of 2 Gyr and a metallicity of [Fe/H] = 0.19 dex (metal-rich relative to the Sun). From Earth, HAT-P-39 shines at apparent V-band magnitude 12.282 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere.

Discovery Facility: HATNet · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).